1. Field of the Invention
The present invention relates to a method of bonding porous members together and, more particularly, to a method which utilizes, as a brazing material, a metallic material containing an eutectic alloy which in turn contains an element having a superior diffusion property to porous metallic materials. The invention is also concerned with a product which includes porous members bonded by such a method.
2. Description of the Prior Art
Various methods have been proposed for bonding porous members such as those made of sintered alloys. For instance, there has been proposed a method in which two members each consisting of compacted powders or, alternatively, one member consisting of compacted powders and the other member made of a sintered material, are bonded by being heated and sintered together while they are held in a mutually fitting relation. A typical example of this method is disclosed in Japanese Pat. Laid-Open No. 57-89412. According to another method proposed hitherto, two porous members are bonded together through a brazing material by making use of peritectic reaction as taught, for example, by Japanese Patent Publication No. 58-34524.
Generally, bonding two members in solid phase by sintering essentially requires that the two members to be bonded be heated while they are pressed in close contact with each other at their bonding surfaces. Various methods have been proposed to achieve such a condition. For instance, it has been proposed to shape two members such that they have complementary or mating configurations. It has also been proposed to select the materials of two members such that the outer member exhibits a greater contraction than the inner member. These methods, however, are applicable only to specific cases and cannot be used broadly as a generic measure.
Problems are also encountered in the known methods for bonding two porous members through a brazing material by making use of peritectic reaction. For example, when a continuous heating furnace of mesh belt type or pusher type is used for heating two porous members to be bonded, these members tend to be offset from each other during the heating process due to impact and vibration imparted by the conveyor device of the furnace since the two cannot be securely fitted together under a high temperature. In addition, the mechanical property of the product is liable to be impaired due to coarsening of the grain structures of two members, due to the fact that the bonding is effected at a high temperature.
Furthermore, since the pores of two members are filled with the brazing material, a large amount of brazing material is consumed and the advantages peculiar to the porous material are impaired because the pores are lost. Finally, it is to be pointed out that the strength of bonding attained by this method is generally insufficient.